Adreonna RaineyUrban trees do so much more than make our campus look beautiful. They filter the air, cool the ground, and improve our mental well-being. But many of the trees at the University of Kentucky are under attack from an invasive pest. Graduate student Zoë York, a senior technician in the Wilson Urban Landscape Entomology Laboratory, is researching how planting the right plants in the right places might be key to protecting city trees and making our shared green spaces healthier.
Calico scale (Eulecanium cerasorum), an invasive sap sucking insect, has infested most of the honey locust trees on campus. Some of the worst damage is visible along S Limestone near the hospitals. But these infestations aren’t random; they’re directly linked to urban conditions that weaken our trees and favor pests.
“The urban heat island effect speeds up pest reproduction… water-stressed trees produce more attractive sap, and—critically—there’s a lack of natural enemies due to simplified vegetation,” York explained. “Most urban trees, including those on campus, are surrounded by grass and little else. In agriculture, we know that planting flowering plants near crops helps attract and support beneficial insects—like predators and parasitoids—that naturally control pest populations.”
In the late spring of 2024, two flowering shrub species were planted underneath 17 calico scale-infested honey locust trees that previously had no vegetation underneath them. After planting the shrubs, York checked each tree for scale insects, measured how many were being attacked by beneficial insects, and studied how active predators were in each area. She ran these early experiments using sentinel prey—live or fake insects that scientists place in the field to measure how much predators are eating. On trees without added plantings, only about a quarter of the prey were eaten. But when shrubs were added, nearly three-quarters were taken out.
This year, York’s project focuses on one big question: if planting more shrubs brings in more predators, will the trees actually end up with fewer calico scale pests?
To measure how well natural enemies were keeping calico scale in check, York collected twigs and leaves from each tree and looked at how many scales had been parasitized. The difference was dramatic—on trees with shrubs, nearly half of the scales were parasitized, while on trees with no shrubs, only a tiny fraction were.
“These are still early results,” York explained, “but they’re really promising. We still have another year of research ahead, but so far the shrubs seem to be making a big difference.”
“This project has the potential to benefit the entire student body and campus community. By supporting healthier trees, we’re also supporting healthier students. Healthy trees and shrubs contribute to cleaner air, cooler, shaded walkways, and improved mental and physical well-being. Studies even show that vegetation on campuses is linked to higher academic performance—so greener spaces can literally help students get better grades.” York said.
In short: a few well-placed flowering plants could mean healthier trees, a healthier campus, and healthier students.
